Raw materials of biological origin are potential sources of various biofuels or biofuel components. These raw materials can be converted to biofuels by feeding the raw material through a catalytic reactor by contacting it simultaneously with gaseous hydrogen. The resulting product is drawn off from the reactor as a product stream which can be further fractionated for example by distillation to form biofuel/biofuel components.
There are however various problems related to production processes of biofuels from the raw materials of biological origin, such as poisoning and clogging of the catalyst material used in the production processes. There are impurities in the raw materials of biological origin, such as metals and solids that cause the inactivation of the catalyst material or cause coking on the catalyst and prevent it to function properly. In order to prevent the inactivation of the catalyst and to prolong its lifetime, the raw material can be purified and/or pretreated before feeding it to the hydrotreatment process. Purifying of the raw materials of biological origin to be suitable for feeding to a catalytic process is also challenging. Prior art describes various ways of doing this. However, these all have problems and the quality of the raw material is not always on a required level for the catalytic step to be able to function in the most efficient way.
One possibility of purifying and/or pretreating a raw material of biological origin, such as crude tall oil (CTO), which is to be fed to catalytic hydrotreatment processes, is ion-exchange with a cationic and/or anionic ion exchange resin.
Another possibility is to use methods such as adsorption on a suitable material or acid washing to remove alkaline metals and earth alkaline metals (Na, K, Ca). The adsorption material can be catalytically active or inactive. Yet another possibility is to use degumming for removing metals in the feed.
When the raw material of biological origin contains tall oil, depitching of the crude tall oil can also be used to remove impurities from the tall oil. Depitched tall oil is obtained by evaporating crude tall oil, for example by thin-film evaporator. U.S. Pat. No. 5,705,722 describes converting unsaturated fatty acids, for example tall oil fatty acids to naphtha and cetane improvers for diesel fuels. However, this process has disadvantages, for example the yield of biofuel or biofuel components, i.e. naphtha and cetane improvers, is poor. This is due to the fact that in depitching a huge amount of valuable raw material for hydrogenation is lost as residue, i.e. pitch. According to the document, the residue is used as such as fuel for boilers.
Terpene-based materials, such as crude turpentine and turpentine distillation residues can also be used as feed materials in biorefineries. However, at the moment the purity of terpene-based materials received, for example from a pulp mill or thermo mechanical processes, can be such that it is not always suitable as a feed material in a catalytic conversion process. Consequently, nowadays most of the terpene-based material that is not directed to other turpentine converting processes is considered as a waste and it ends up to be burnt in a lime kiln or a recovery boiler or any other boiler such as boilers using light or heavy oil as the fuel.
It has not been suggested in the prior art to purify a mixture of terpene-based material and tall oil-based material by evaporating and to use the fractions recovered from the purification as a feed to catalytic hydroprocessing thereafter.